Pathogens usually found in human brain abscess in normal and in immunosuppressed patients will be used to produce an experimental abscess in dogs by a direct inoculation technique. The contrast enhanced computed tomographic (CT) scan appearance of brain abscess will be investigated in this experimental model which delineates progression of the infection from the cerebritis stage to encapsulation. CT criteria for staging a brain abscess (i.e., degree of encapsulation) will be developed using temporal changes in contrast enhancement, the effect of short-term corticosteroids on contrast enhancement and rapid-sequence dynamic CT scans in conjunction with neuropathologic correlation. New contrast agents with a different mechanism of action will be used to image brain abscess. A critical factor in the development of optimal treatment for brain abscess will depend on a clinically reliable, noninvasive method of histologically staging an abscess; this study will provide such a method.